Jake Dove Honours Thesis Abstract

Neepawa Island, located within the Sioux Lookout greenstone belt of the Western Wabigoon subprovince has been an area of several historical gold occurrences over the past century.  In this study, structural controls of gold mineralization are assessed with an emphasis on microstructural analysis.  The study area on west Neepawa Island is situated at the southern edge of the central volcanic belt, approximately 12km southeast of Sioux Lookout, Ontario near the center of Minnitaki Lake.  Locally, the study area hosts intermediate pyroclastic and mafic volcanic flow units displaying brittle and ductile deformation, pervasive hydrothermal alteration, and metamorphism to the greenschist facies.  Microstructural analysis concluded that gold mineralization is related to non-coaxial deformation of north-south striking, steeply dipping vein set 1, the oldest vein set at the study area.  Gold is concentrate where deformation is greatest in the quartz-carbonate vein and adjacent pyritic halo, approximately parallel to the regional foliation.  Gold mineralization is hosted in microstructures such as subgrain ribbons and microfractures in the quartz veins, as well as microfractures and pressure shadows associated with pyrite.  These brittle and ductile microstructures were produced from competency contrasts during deformation between the mesothermal quartz-carbonate veins, metavolcanic host rock, and syn-deformational pyrite.  Gold-hosting microstructures may be controlled by deformation caused by the sinistral-reverse displacement related to the regional Ruby Island Fault system.